import java.util.Scanner;

/**
 * Created by Salted fish
 * Description:
 * User: 24539
 * Date：2021-07-30
 * Time: 17:56
 */
public class Test10 {
 /*  // public static void main(String[] args) {
        int a =10;
        int b=20;
        System.out.println(add(a,b));
        double n=10.0;
        double m=20.0;
        double z=3.0;
        System.out.println(fid(m,n,z));
    }
    public static int add(int a,int b) {
        return a+b;
    }
    public static double fid(double n,double m, double z) {
        return (n+m+z);
    }*/
    public static void main(String[] args) {
        Scanner sn= new Scanner(System.in);
        int n= sn.nextInt();
        System.out.println(fn(n));
    }
    public static int  fn(int n) {
        if(n == 1 || n == 2) {
            return 1;
        }
        return fn(n-1)+fn(n-2);
    }
}
